This invention relates of a multi-faced extrusion die assembly for an extruder, which facilitates production of extruded pieces having more than one cross-sectional configuration. More particularly, the invention relates to an extrusion die assembly adapted to be mounted on an extruder, with the assembly having a plurality of spaced die plates and including a rotatable diversion valve for directing the flow of thermoplastic material from the extruder to a selected die plate without interrupting the operation of the extruder.
Extruders are widely used in a number of industries, particularly the food industry in which extruders are utilized to produce a variety of products such as snack foods, breakfast cereals, pet foods, and confections. Extruders typically consist of one or more sets of flighted screws which rotate within a barrel and have a die plate mounted across the discharge end of the extruder barrel. Thermoplastic material from the extruder is forced through one or more die openings in the die plate, with the openings having a particular cross-sectional configuration whereby the extrudate has the same single cross-sectional configuration as the die openings. The thermoplastic material extruded through the die openings is cut into pieces of desired length, typically by means of a rotary knife mounted adjacent the outer face of the die plate.
The use of die plates having die openings of more than one cross-sectional configuration is not feasible for it would provide non-uniform flow rates and different flow resistances across the extrusion orifices, resulting in the production of undesirable non-uniform extruded pieces. Thus, the production of extruded pieces having different shapes or sizes requires the use of separate die plates, each having die orifices of one desired cross-sectional configuration. In commercial production operations, when it is desired to change the size or shape of pieces produced from an extruder, the operation of the extruder must be stopped while one die plate is removed and is replaced by another die plate having orifices of the desired size or shape.
Such interruptions in the operation of the extruder have an adverse effect on the production capacity of the extruder and result in the loss of significant amounts of material.